Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove fan/manifold assembly
Remove the burner/baffles assembly

Observation:

Using the servicing kit if available (part number 740-549), inspect the burner/baffles
for debris, damage and good general condition and are fitted correctly.
If burner/baffle condition is ok do not reassemble as it may need to
be removed for further tests.
Note:
This component requires the air/gas manifold to be removed
therefore the gasket between the gas air manifold and the
heat exchanger must be changed.
Refer to the safety notice on the side of the
heat exchanger for information on reassembly.